JP2021070075A - Cutting tool including hard coat - Google Patents

Abstract

To render more finer crystals of an Si-containing coat that is a second layer of a hard coat, for achieving improved hardness and durability.SOLUTION: A cutting tool has a hard coat 2 on a base material 1 of a cutting part. The hard coat 2 coating the base material 1 has a laminated structure of a multiple laminate layer 3 to be a first layer, a second layer 4 and a third layer 5. The multiple laminate layer 3, laid directly over the base material 1, has a plurality of first films 7 composed of thin layers TiSiN and a plurality of second films 8 composed of TiAlCrN alternately laid on top of each other. Furthermore, on the surface of the multiple laminate layer 3, the second layer 4 composed of TiSiN and the second layer 4 composed of TiAlCrN are laminated.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cutting tool provided with a hard coating that covers the blade portion of the cutting tool made of a metal material or the like.

Conventionally, with the speeding up and drying of cutting and the hardness of the workpiece, a hard coating with more oxidation resistance and long life has been replaced with cutting tools such as ball end mills coated with TiAlN coating. With cutting tools are used. For example, as a cutting tool coated with this kind of hard coating, a cutting tool coated with a Si-containing coating obtained by adding Si to TiN or the like is adopted.
As such a cutting tool, the one described in Patent Document 1 is known. In this coated cutting tool, as shown in FIG. 7, the surface of the cemented carbide base material 100 of the cutting tool is coated with a first layer 101 made of a Si-free coating which is a nitride of TiAlCr (TiAlCrN). The surface thereof is coated with a second layer 102 of a Si-containing coating mainly composed of TiSi nitride (TiSiN). Further, the surface of the second layer 102 has a hard coating 104 having a three-layer structure coated with the third layer 103 made of TiAlCrN.

The hard coating 104 has a consistent crystal structure by alternately laminating TiAlCrN-based coatings and TiSiN-based coatings. Further, the adhesion is improved while maintaining the wear resistance and oxidation resistance of TiSiN. Moreover, by forming the first layer 101 and the third layer 103 with a Si-free coating, high hardness and good oxidation resistance can be obtained. Further, since a fine and dense columnar crystal crystal structure is formed, the TiSiN layer of the second layer 102 is said to have high adhesion and wear resistance due to accelerated epitaxial growth.

Japanese Unexamined Patent Publication No. 2008-264971

However, the hardness of the TiAlCrN-based coating of the first layer 101 realized from the structure of the hard coating described in Patent Document 1 described above, and the Si-containing coating of the second layer 102 epitaxially grown according to the crystal size of the TiAlCrN-based coating. In terms of hardness, there is a drawback that the hardness is not sufficient when cutting a work material having a higher hardness, and the crystal refinement and durability are not sufficient.

The present invention has been made in view of such circumstances, and a cutting tool provided with a hard coating capable of improving hardness and durability by making the crystals of the Si-containing coating, which is the second layer of the hard coating, finer. The purpose is to provide.

In the cutting tool provided with the hard coating film according to the present invention, the base material is alternately laminated with a first film made of a thin layer of Si-containing nitride and a second film made of AlCr-containing nitride laminated on the surface of the base material. A first layer, which is a multi-layered layer in which a plurality of layers are laminated, and a second layer of a Si-containing nitride laminated on the surface of the multi-layered layer and having a thickness larger than that of the first film and the second film are provided. It is characterized by that.
According to the present invention, as a multi-layered layer laminated on the surface of a base material, a thin layer of a first film of Si-containing nitride and a second film of AlCr-containing nitride are alternately laminated a plurality of times to form columnar crystals. Growth is suppressed and the crystal size is reduced. The second film on the upper side of the first film has a smaller crystal size following the first film with a fine crystal structure, and the growth of crystals that progress toward the surface is caused by the first film on the upper side of the second film. Suppress. As a result of this repetition, the columnar crystals can be miniaturized and a high-hardness multi-layered layer can be formed. Moreover, the second layer of the Si-containing nitride coated on the upper side of the multi-layered layer also promotes epitaxial growth following the multi-layered layer, and the crystal becomes finer and becomes higher in hardness. The sharpness of the cutting edge of the cutting tool is improved and the durability is improved by making the crystals of the hard coating composed of the first layer of the multiple laminated layer and the second layer finer.

Further, it is preferable that the third layer of the TiAlCr-containing nitride is laminated on the surface of the second layer of the Si-containing nitride.
The crystals of the Si-containing nitride in the second layer are made finer and harder, which makes it easier for chipping to occur. However, since the TiAlCr-containing nitride in the third layer has high toughness, it prevents chipping in the second layer and resists chipping. Improves defectability and durability.

Further, it is preferable that the average film thickness of each of the first film and the second film constituting the multiple laminated layer is in the range of 10 to 60 nm, and the overall layer thickness is set to 4.0 μm or less.
By alternately laminating a plurality of layers of the first film and the second film, it is possible to promote finer crystals and higher hardness of these films and the second layer above them.

Further, it is preferable that the first film of the multilayer layer is TiSiN and the second film is TiAlCrN.
As a result, it is possible to promote the miniaturization and high hardness of the crystals of the first film and the second film of the multi-layered layer.
When the film thickness of the multiple laminated layer is T1 and the film thickness of the second layer is T2, the ratio T2 / T1 of the film thickness of the first layer to the film thickness of the second layer is 0.2 ≦ T2 / T1. It is preferable that ≦ 10.0 and the total film thickness (T1 + T2) of the first layer and the second layer is 6 μm or less.

According to the cutting tool provided with the hard coating according to the present invention, a multi-layered layer in which a thin layer of the first film of Si-containing nitride and the second film of AlCr-containing nitride are alternately laminated is provided on the base material. Therefore, the growth of columnar crystals is suppressed, and fine and high-hardness thin layers can be laminated. Moreover, the Si-containing nitride of the second layer coated on the surface of the multi-layered layer promotes epitaxial growth in the same manner as the multi-layered layer, and can promote the miniaturization and high hardness of the crystal.

It is a schematic diagram which shows the hard coating which covers the base material of the cutting tool by embodiment of this invention. It is a schematic diagram which shows the film forming apparatus of a hard film according to an embodiment. It is the figure of the EDS line which shows the measurement place of the multi-layered layer and the concentration of each element at the position, (a) is the figure which shows the upper part of a multi-layered layer, (b) is a figure which shows the central part, (c) is the figure which shows the lower part. is there. (A) is a diagram of the coating of the multi-layered layer in the embodiment, and (b) is a diagram of the coating of the conventional TiAlCrN layer. (A) is a diagram of the coating of the TiSiN layer in the embodiment, and (b) is a diagram of the coating of the conventional TiSiN layer. It is a figure of the cutting edge part after processing each work for a predetermined time by the end mill according to an embodiment and the end mill according to a conventional example. It is a figure which shows the hard film coated on the conventional base material.

Hereinafter, the hard coating formed on the cutting edge portion of the cutting tool according to the embodiment of the present invention will be described with reference to FIGS. 1 to 6.
In the embodiment of the present invention, as shown in FIG. 1, a cutting tool such as a ball end mill is used as a tool, and a hard coating 2 is coated on a base material 1 which is a cutting edge portion of the cutting tool. On the surface of the base material 1 of the cutting tool, as a hard coating film 2, a multi-layered layer 3 as a first layer in which a plurality of types of thin first film 7 and a second film 8 are alternately coated, and a first film 7 The second layer 4 and the third layer 5 having a film thickness larger than that of the second film 8 are laminated to form a coating.

For example, cemented carbide, high-speed steel or cermet is used as the base material 1. In the multilayer layer 3, a plurality of TiSi nitrides (TiSiN) as the first film 7 and TiAlCr nitrides (TiAlCrN) as the second film 8 are alternately laminated on the base material 1. .. The TiSiN of the first film 7 forms fine crystals, and the average film thickness is grown into a thin layer of, for example, 10 nm to 60 nm.
Since TiALCrN of the second film 8 on the first film 7 follows the crystal size of the lower TiSiN, the crystal becomes smaller. By coating the first film 7 of the next TiSiN at the stage of thinning, the first film 7 and the second film 8 can be sequentially laminated with a thin film thickness to form the multiple laminated layer 3.

Since TiAlCrN is a Si-free coating and TiSiN is a Si-containing coating, its hardness is larger than that of TiAlCrN. Each of the first film 7 and the second film 8 is a thin layer having an average film thickness in the range of, for example, 10 nm to 60 nm, and TiSiN is coated as the second layer 4 coated on the multi-layered layer 3, and above the multiple laminated layers 3. TiAlCrN is coated as the third layer 5 of the above. The second layer 4 and the third layer 5 are single layers each made of a single material, and have a larger film thickness than the first film 7 and the second film 8.

In the multilayer layer 3, a thin layer of TiSiN is laminated as the first film 7 on the base material 1, and TiAlCrN is laminated as the second film 8 on the surface thereof. Moreover, by coating TiSiN again with the second film 8 of TiAlCrN in a thin layer state, TiAlCrN is also coated as a thin layer. In this way, the multiple laminated layer 3 can be formed by alternately laminating a plurality of layers of the first film 7 and the second film 8. By alternately laminating the first film 7 and the second film 8 of the thin layer, the crystals of the multi-layered layer 3 are miniaturized to have high strength.
In this case, the film thickness of the entire multilayer layer 3 is, for example, in the range of 0.3 μm to 4.0 μm, preferably in the range of 0.5 μm to 3.0 μm. Although the first film 7 and the second film 8 are formed to have different thicknesses, they may have the same thickness. Since TiSiN is originally a fine crystal, it is possible to prevent TiAlCrN from becoming a large crystal by alternately sandwiching the crystal with TiAlCrN.

The number of layers of the first film 7 and the second film 8 of the multi-layer layer 3 can be set as appropriate, and varies depending on the size of the cutting tool. The first film 7 is attached to the base material 1 of the multiple laminated layer 3, and the first film 7 is also attached to the uppermost portion. However, instead of this configuration, the stacking arrangement order of the first film 7 and the second film 8 may be reversed, the second film 8 is attached to the base material 1, and the second film 8 is also attached to the uppermost portion. You may. If only one of the first film 7 and the second film 8 is attached, the crystal size becomes large because it becomes a single layer.

Further, TiSiN as the second layer 4 coated on the multiple laminated layer 3 originally has a high hardness, but the first film 7 and the second film 8 of the multiple laminated layer 3 having a finer crystal size Similarly, epitaxial growth is promoted, and the crystal size becomes finer, so that the hardness becomes higher. The film thickness of the second layer 4 is set in the range of, for example, 0.5 μm to 4.0 μm.
TiAlCrN as the third layer 5 laminated on the TiSiN of the second layer 4 is formed to have a smaller film thickness than, for example, the second layer 4, and has high toughness. The TiSiN of the second layer 4 is finely crystallized and the hardness is increased, which causes a characteristic that it is easily broken during cutting. However, the TiAlCrN of the third layer 5 coated on the TiSiN has high toughness, so that the cutting edge is broken. Can be suppressed.

A method of forming a film of a cutting tool having a hard film 2 having the above-described configuration will be described with reference to FIG.
The film forming apparatus according to the embodiment is performed by, for example, an arc discharge apparatus 10 using a physical vapor deposition method (PVD). The table 12 is rotatably arranged in the container 11 of the arc discharge device 10, and the first jig 13 and the second jig 14 are rotatably arranged at positions on the table 12 facing 180 °. .. Base materials 1A and 1B are installed on the first jig 13 and the second jig 14, respectively. The base material 1 may be fixed by providing only one jig.
Further, a metal TiSi to be evaporated as a first target 15 is installed at one of the positions facing 180 ° on the outside of the table 12, and a metal TiAlCr to be evaporated as a second target 16 is installed at the other position with each target. A heater for heating the base material 1A and the base material 1B is installed at a position where they do not interfere with each other. Moreover, the container 11 is connected to the vacuum pump P to evacuate the inside of the container 11. Further, a plurality of gases can be supplied into the container 11.

Then, the base materials 1A and 1B installed on the table 12 in the depressurized container 11 of the arc discharge device 10 revolve on the table 12 while rotating on the first jig 13 and the second jig 14. The table 12, the first jig 13, and the second jig 14 can rotate in the same direction, but may rotate in opposite directions.
After the container 11 is evacuated from the atmospheric pressure by the vacuum pump P, the base material 1A and the base material 1B are heated by a heater, and a bias voltage is further applied to the base material 1A and the base material 1B, and then argon ions or a target. The base material 1A and the base material 1B are cleaned with the derived metal ions.
Then, at a position where the base material 1A rotates in the vicinity of the metal TiSi of the first target 15, for example, a voltage is applied between the metal TiSi of the first target 15 as an evaporation source and the base material 1A to ionize the metal evaporated. Then, the first film 7 is formed on the base material 1A by adhering it to the surface of the base material 1A to which the bias voltage is applied.

Further, at a position where the base material 1B rotates in the vicinity of the metal TiAlCr of the second target 16, for example, a voltage is applied between the metal TiAlCr of the second target 16 as an evaporation source and the base material 1B to ionize the metal evaporated. Then, the second film 8 is formed on the base material 1B by adhering it to the surface of the base material 1B to which the bias voltage is applied.
In this case, since the first jig 13, the second jig 14, the first target 15, and the second target 16 are provided at positions facing each other by 180 degrees, the first target 15 and the second target 16 are simultaneously discharged. Each metal ion is evaporated and attached to the base materials 1A and 1B, respectively. However, the first jig 13, the second jig 14, the first target 15, and the second target 16 are installed at appropriate angles different from 180 degrees, and the first target 15 and the second target 16 are individually arranged at different timings. May be discharged to.

Next, when the base material 1A is located near the metal TiAlCr of the second target 16, the metal ions evaporated by applying a voltage between the metal TiAlCr of the second target 16 and the base material 1A are used as the base material 8 as the base material 8. It adheres to the surface of the first film 7 of 1A and coats it. Further, when the base material 1B is located in the vicinity of the metal TiSi of the first target 15, the metal ions evaporated by applying a voltage between the metal TiSi of the first target 15 and the base material 1B are used as the first film 7 and the base material 1B is used. It is attached to the surface of the second film 8 and coated.
At that time, since the first film 7 and the second film 8 are laminated with thin layers having an average film thickness of 10 to 60 nm, preferably 10 to 30 nm, respectively, the crystal size becomes small and the hardness becomes high. By repeating this operation, a plurality of first films 7 and a plurality of second films 8 are alternately laminated a plurality of times on the surfaces of the two types of base materials 1A and 1B every half rotation of the table 12, and an appropriate plurality of layers are multiplexed. The laminated layer 3 is formed.

In the next step, a voltage is applied only to the metal TiSi of the first target 15 to evaporate the metal ions, and the TiSiN of the second layer 4 is formed on the multiple laminated layers 3 of the base materials 1A and 1B on the rotating table 12. Cover. Since the film thickness of TiSiN as the second layer 4 is about 0.5 μm to 4.0 μm, which is larger than the film thickness of the first film 7 and the second film 8 of the multi-layer laminated layer 3, metal ions are generated over a longer period of time. Evaporate.
Next, a voltage is applied only to TiAlCr of the second target 16 to evaporate the metal ions, and a film thickness of about 0.2 μm to 0.8 μm is applied on the second layer 4 of the base materials 1A and 1B on the rotating table 12. The third layer 5 having TiAlCrN is coated with TiAlCrN. In this way, the three layers of the hard coating 2 can be laminated on the base materials 1A and 1B, respectively.

When the film thickness of the multi-layered layer 3 which is the first layer is T1 and the film thickness of the second layer 4 is T2, the ratio of the film thickness of the multi-layered layer 3 to the film thickness of the second layer 4 T2 / T1 is preferably 0.2 ≦ T2 / T1 ≦ 10.0. When T2 / T1 is less than 0.2, the wear resistance of the high hardness TiSiN is not sufficiently exhibited, and the durability against the high hardness work material is inferior. On the other hand, if it exceeds 10.0, chipping is likely to occur at an early stage, and the quality of the machined surface deteriorates as abnormal wear progresses.
Moreover, the total film thickness (T1 + T2) of the multiple laminated layer 3 and the second layer 4 is preferably 6 μm or less. If (T1 + T2) exceeds 6 μm, self-destruction due to internal stress and early peeling will occur, resulting in reduced durability.

Next, specific examples of the cutting tool with the hard coating 2 formed by the present embodiment will be described with reference to FIGS. 3 to 5 as examples. The measurement result of the element will be described as a specific example of the hard coating 2 in which the uppermost layer and the lowermost layer are coated with the multi-layered layer 3 of TiSiN on the base material 1 (see FIG. 1).

3 (a), (b), and (c) show EDS (energy dispersive X-ray spectroscopy) of TEM (transmission electron microscope) for the upper, central, and lower regions P1, P2, and P3 of the multilayer layer 3. It is the figure which measured the concentration of each element with a vessel) and extracted the line. In this case, since a specific portion of the multi-layered layer 3 as a sample can be evaluated pinpointly during high-magnification observation with a TEM, a minute region on the order of nm was analyzed.
FIG. 3A shows the elements near the boundary between the upper part of the multiple laminated layer 3 and the TiSiN of the second layer 4 in the hard coating 2. FIG. 3B shows the elements in the central portion of the multi-layered layer 3, and FIG. 3C shows the elements near the boundary between the lower portion of the multi-layered layer 3 and the base material 1.

Next, FIGS. 4 and 5 are cross-sectional images showing the crystal structure of the hard coating 2.
FIG. 4A is a cross-sectional image of the multiple laminated layer 3 in the embodiment, and FIG. 4B is a cross-sectional image of TiAlCrN of the first layer 101 in the conventional hard coating shown in FIG.
The component ratios a and b of the metal components of TiaSibN of the first film 7 and the second layer 4 in the examples are as follows in terms of atomic ratio (at%), and TicAldCre of the second layer 4 and TifArgCrh of the third layer are The atomic ratio (at%) is as follows.
a = 0.78, b = 22
c = 0.16, d = 0.57, e = 0.27
f = 0.16, g = 0.57, h = 0.27

The TijAlkCrl of the first layer 101, the TimSin of the second layer 102, and the TioAlpCrq of the third layer 103 in the conventional example are as follows in atomic ratio (at%).
j = 0.16, k = 0.57, l = 0.27
m = 0.78, n = 0.22
o = 0.16, p = 0.57, q = 0.27

In the cross-sectional images of FIGS. 4A and 4B, the boundary between white and black indicated by contrast indicates one unit of crystal, and the crystal unit t1 of the example is about 1/3 of the crystal unit t2 of the conventional example. It is the size of.
Further, FIG. 5A is a cross-sectional image showing the TiSiN layer of the second layer 4 in the embodiment, and FIG. 5B is a cross-sectional image showing the TiSiN layer of the second layer 102 in the conventional example shown in FIG. is there. In the cross-sectional images of FIGS. 5A and 5B, the boundary between white and black indicated by contrast indicates one unit of crystal, and the columnar crystal unit t1 of the example is 1 / of the columnar crystal unit t2 of the conventional example. It can be recognized that the size is about 2.
According to the test results, the average value of each columnar crystal unit t1 in the multi-layered layer 3 and the second layer 4 can be miniaturized to 100 nm or less, for example, 30 nm in the width direction orthogonal to the longitudinal growth direction of the columnar crystal.

Next, FIG. 6 shows the results of cutting by the ball end mill provided with the hard coating 2 according to the embodiment and the ball end mill provided with the hard coating 104 according to the conventional example shown in FIG. The test results show the degree of chipping and wear of the cutting edge of each ball end mill after cutting. The ball end mills of the examples and the conventional examples have the same dimensions, and the base material is a cemented carbide.
The first work is a high-performance powder high-performance (trade name HAR40 manufactured by Hitachi Metals Tool Steel Co., Ltd.), and its hardness is 64 HRC in Rockwell hardness. The second work is SKD11 series die steel (trade name DC53 manufactured by Daido Steel Co., Ltd.), and its hardness is Rockwell hardness of 60 HRC.

The cutting conditions of the first workpiece are rotation speed n: 20,000 ^{min -1} , feed speed Vf: 1,600 mm / min, 1-blade feed fz: 0.04 mm / tooth, axial depth of cut up x radial direction. Cutting amount ae: 0.15 mm × 0.3 mm. The cutting conditions of the second work are n: 25,000 ^{min -1} , Vf: 2,000 mm / min, fz: 0.04 mm / tooth, ap × ae: 0.2 mm × 0.3 mm.

FIG. 6 shows the state of the cutting edge after the first work is machined with the ball end mill of the embodiment and the ball end mill of the conventional example for 70 minutes. In the figure, in the embodiment, although there is a small amount of wear on the cutting edge and the flank, no defect or the like is observed. On the other hand, in the conventional example, the cutting edge and the flank are defective and are greatly worn.
The state of the cutting edge after processing the second work with the ball end mill of the embodiment and the ball end mill of the conventional example for 5 hours is shown. In the figure, in the embodiment, only a small amount of wear is observed on the cutting edge and the flank, and no defect is observed. On the other hand, in the conventional example, the cutting edge and the flank are heavily worn, and some defects are observed.

As described above, according to the cutting tool with a hard coating according to the present embodiment, a multi-layered layer 3 in which a plurality of thin TiSiN first films 7 and TiAlCrN second films 8 are alternately laminated is provided on the surface of the base material 1. The second layer 4 of TiSiN and the third layer 5 of TiAlCrN were laminated and coated on the second layer 4 of TiSiN. Therefore, the crystal size of the thin first film 7 and the second film 8 is small and the hardness is high, and the second layer 4 of TiSiN coated on the multi-layer 3 is used for the crystal refinement of the multi-layer 3. Similarly, epitaxial growth is promoted, the crystal is refined, and the hardness is increased. Therefore, the sharpness, abrasion resistance, and fracture resistance of the cutting edge can be improved.
Further, since the third layer 5 of TiAlCrN is coated on the second layer 4, the crystals of the third layer 5 having high toughness are bonded to the second layer 4 which has high hardness and is likely to cause chipping, and chipping is performed. Can be suppressed. In this respect as well, wear resistance and fracture resistance can be improved.

Although the cutting tool provided with the hard coating 2 according to the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and various different modes are provided without departing from the spirit of the present invention. It goes without saying that the above mode can be adopted. All of these are included in the scope of the present invention.
Next, other embodiments and modifications of the present invention will be described, but the same or similar parts and parts of the above-described embodiments will be described using the same reference numerals.

In the above-described embodiment, with respect to the hard coating film 2, the multiple laminated layers 3 are alternately laminated with TiSiN and TiAlCrN as the first film 7 and the second film 8, and the second layer 4 is TiSiN and the third layer 5 is TiAlCrN. .. However, the present invention is not limited to such a configuration, and those having different coating materials for the multiple laminated layer 3, the second layer 4, and the third layer 5 may be adopted.
Further, the first film 7 and the second layer 4 of the multiple laminated layer 3 may be Si-containing nitrides, and Ti may be replaced with or another element containing Ti may be used. Further, the second film 8 and the third layer 5 of the multiple laminated layer 3 may be AlCr-containing nitrides and Si-free nitrides, and in this case as well, Ti is not contained or Ti is contained in another element. May be used.

In the above-described embodiment, the multiple laminated layer 3 and the second layer 4 of the first layer on the base material 1 may be formed by repeating the lamination a plurality of times.
Further, in the above-described embodiment, cutting is performed using a ball end mill as an example of a cutting tool, but the cutting tool provided with the hard coating 2 in the present invention is not limited to the ball end mill. Needless to say, it can be applied to other turning tools such as drills and turning tools such as cutting tools.

1, 1A, 1B Base material 2 Hard coating 3 Multiple laminated layer 4 Second layer 5 Third layer 7 First film 8 Second film 10 Arc discharge device 12 Table 15 First target 16 Second target

Claims (5)

With the base material
The first layer, which is a multi-layered layer in which a first film made of a thin Si-containing nitride and a second film made of an AlCr-containing nitride alternately laminated on the surface of the base material, are laminated.
A second layer of Si-containing nitride that is laminated on the surface of the multiple laminated layer and has a film thickness larger than that of the first film and the second film,
A cutting tool with a hard coating characterized by being equipped with. The cutting tool provided with the hard coating according to claim 1, wherein the third layer of the TiAlCr-containing nitride is laminated on the surface of the second layer of the Si-containing nitride. According to claim 1 or 2, the first film and the second film constituting the multiple laminated layer have an average film thickness in the range of 10 nm to 60 nm and are set to a layer thickness of 4.0 μm or less as a whole. Cutting tool with the described hard coating. The cutting tool provided with the hard coating according to any one of claims 1 to 3, wherein the first film of the multi-layer is TiSiN and the second film is TiAlCrN. When the film thickness of the multiple laminated layer is T1 and the film thickness of the second layer is T2, the ratio T2 / T1 of the film thickness of the first layer to the film thickness of the second layer is 0.2 ≦ T2. / T1 ≦ 10.0, and the total film thickness (T1 + T2) of the first layer and the second layer is 6 μm or less. ..

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